scholarly journals Coordination of Rheb lysosomal membrane interactions with mTORC1 activation

F1000Research ◽  
2020 ◽  
Vol 9 ◽  
pp. 450 ◽  
Author(s):  
Brittany Angarola ◽  
Shawn M. Ferguson
Keyword(s):  
Small Gtpase ◽  
Membrane Targeting ◽  
Activation Process ◽  
Membrane Interactions ◽  
Mechanistic Target Of Rapamycin ◽  
Activation Mechanisms ◽  
Molecular Machinery ◽  
Growth Promoting ◽  
Prenylated Proteins ◽  
Mtorc1 Activation

A complex molecular machinery converges on the surface of lysosomes to ensure that the growth-promoting signaling mediated by mechanistic target of rapamycin complex 1 (mTORC1) is tightly controlled by the availability of nutrients and growth factors. The final step in this activation process is dependent on Rheb, a small GTPase that binds to mTOR and allosterically activates its kinase activity. Here we review the mechanisms that determine the subcellular localization of Rheb (and the closely related RhebL1 protein) as well as the significance of these mechanisms for controlling mTORC1 activation. In particular, we explore how the relatively weak membrane interactions conferred by C-terminal farnesylation are critical for the ability of Rheb to activate mTORC1. In addition to supporting transient membrane interactions, Rheb C-terminal farnesylation also supports an interaction between Rheb and the δ subunit of phosphodiesterase 6 (PDEδ). This interaction provides a potential mechanism for targeting Rheb to membranes that contain Arl2, a small GTPase that triggers the release of prenylated proteins from PDEδ. The minimal membrane targeting conferred by C-terminal farnesylation of Rheb and RhebL1 distinguishes them from other members of the Ras superfamily that possess additional membrane interaction motifs that work with farnesylation for enrichment on the specific subcellular membranes where they engage key effectors. Finally, we highlight diversity in Rheb membrane targeting mechanisms as well as the potential for alternative mTORC1 activation mechanisms across species.

scholarly journals A spatially regulated GTPase cycle of Rheb controls growth factor signaling to mTORC1

2018 ◽  
Author(s):  
Marija Kovacevic ◽  
Christian H. Klein ◽  
Lisaweta Roßmannek ◽  
Antonios D. Konitsiotis ◽  
Angel Stanoev ◽  
...  
Keyword(s):  
Growth Factors ◽  
Growth Factor ◽  
Small Gtpase ◽  
Target Of Rapamycin ◽  
Growth Factor Signaling ◽  
Nucleotide Exchange ◽  
Gtpase Activating Protein ◽  
Mechanistic Target Of Rapamycin ◽  
Gtpase Cycle ◽  
Mtorc1 Activation

ABSTRACTGrowth factors initiate anabolism by activating mechanistic target of rapamycin complex 1 (mTORC1) via the small GTPase Rheb. We show that the GTPase cycle of Rheb is spatially regulated by the interaction with its GDI-like solubilizing factor (GSF) – PDEδ. Arl2-GTP mediated localized release of cytosolic Rheb-GTP from PDEδ deposits it onto perinuclear membranes where it forms a complex with mTORC1. The membrane associated GTPase activating protein (GAP) TSC2 hydrolyzes Rheb-GTP, weakening the interaction with mTOR. Rheb-GDP is readily released into the cytosol where it is maintained soluble by interaction with PDEδ. This solubilized Rheb is re-activated by nucleotide exchange to be re-deposited by Arl2-mediated release onto perinuclear membranes. This spatial GTPase cycle thereby enables mTORC1 activation to be solely controlled by growth factor induced inactivation of TSC2. The coupling between mTOR activation and spatially regulated Rheb nucleotide exchange makes growth factor induced proliferation critically dependent on PDEδ expression.

scholarly journals mTORC1 Restricts Hepatitis C Virus Replication Through ULK1-mediated Suppression of miR-122 and Facilitates Post-replication Events

2018 ◽  
Author(s):  
Manish Kumar Johri ◽  
Hiren Vasantrai Lashkari ◽  
Dhiviya Vedagiri ◽  
Divya Gupta ◽  
Krishnan Harinivas Harshan
Keyword(s):  
Hepatitis C Virus ◽  
Hepatitis C ◽  
Viral Infection ◽  
Virus Replication ◽  
Viral Rna ◽  
Hcv Rna ◽  
Significant Drop ◽  
Mechanistic Target Of Rapamycin ◽  
Mtorc1 Activation ◽  
Rna Levels

ABSTRACTMechanistic target of rapamycin (mTOR) is an important kinase that assimilates several upstream signals including viral infection and facilitates appropriate response by the cell through two unique complexes mTORC1 and mTORC2. Here, we demonstrate that mTORC1 is activated early during HCV infection as antiviral response. Pharmacological inhibition of mTORC1 promoted HCV replication as suggested by elevated levels of HCV (+) and (-) RNA strands. This was accompanied by significant drop in extracellular HCV RNA levels indicating defective post-replication stages. The increase in viral RNA levels failed to augment intracellular infectious virion levels, suggesting that mTORC1 inhibition is detrimental to post-replication steps. Lower infectivity of the supernatant confirmed this observation. Depletion of Raptor and ULK1 accurately reproduced these results suggesting that mTORC1 imparted these effects on HCV through mTORC1-ULK1 arm. Interestingly, ULK1 depletion resulted in increased levels of miR-122, a critical host factor for HCV replication, thus revealing a new mechanism of regulation by ULK1. The binary effect of mTORC1 on HCV replication and egress suggests that mTORC1-ULK1 could be critical in replication: egress balance. Interestingly we discover that ULK1 depletion did not interfere with autophagy in Huh7.5 cells and hence the effects on HCV replication and post-replication events are not resultant of involvement of autophagy. Our studies demonstrate an overall ULK1 mediated anti-HCV function of mTORC1 and identifies an ULK1-independent autophagy that allows HCV replication in spite of mTORC1 activation.

Abstract 102: Cardiac-specific Overactivation of the Mechanistic Target of Rapamycin Complex 1 Induces Metabolic, Structural and Functional Remodeling

2015 ◽  
Vol 117 (suppl_1) ◽  
Author(s):  
Giovanni Davogustto ◽  
Rebecca Salazar ◽  
Hernan Vasquez ◽  
Heinrich Taegtmeyer
Keyword(s):  
Glucose Uptake ◽  
Glucose Transporter ◽  
Target Of Rapamycin ◽  
Glycolytic Intermediate ◽  
Glucose Transporter 1 ◽  
Structural Remodeling ◽  
Mechanistic Target Of Rapamycin ◽  
Metabolic Remodeling ◽  
Functional Remodeling ◽  
Mtorc1 Activation

The heart remodels metabolically and structurally before it fails. Metabolically, the heart increases its reliance on carbohydrates for energy provision. Structurally, the heart hypertrophies to sustain increased hemodynamic stress. There is evidence suggesting that the activation of the mechanistic Target Of Rapamycin Complex 1 (mTORC1) pathway is closely tied to glucose uptake by the heart to drive the metabolic and structural remodeling. We have previously shown that with insulin stimulation or increases in workload, the glycolytic intermediate glucose 6-phosphate (G6P) is required to activate mTORC1. Sustained mTORC1 activation leads, in turn, to ER stress and contractile dysfunction. Studies by others in the kidney have shown that mTORC1 activation upregulates glucose transporter 1 (Glut1) expression and glucose uptake. We therefore test the hypothesis that chronic mTORC1 overactivation results in G6P accumulation, and precedes structural and functional remodeling in the heart. We developed mice with inducible, cardiac-specific deficiency of the protein tuberin (TSC2), a member of the tuberous sclerosis complex, the principal inhibitor of mTORC1. Intracellular G6P concentrations were measured enzymatically. Immunoblotting was performed on protein markers to confirm activation of mTORC1 downstream targets and of the unfolded protein response. Histologic analysis were performed to assess structural changes. Serial echocardiograms were performed to evaluate cardiac function. The results indicate that chronic mTORC1 activation through inducible, cardiac-specific deletion of TSC2 is accompanied by G6P accumulation and metabolic remodeling. Metabolic remodeling precedes structural and functional remodeling. We suggest that in the heart, sustained mTORC1 activation is a key driver of metabolic and structural remodeling.

High-intensity muscle contraction-mediated increases in Akt1 and Akt2 phosphorylation do not contribute to mTORC1 activation and muscle protein synthesis

2020 ◽  
Vol 128 (4) ◽  
pp. 830-837 ◽  
Author(s):  
Yuki Maruyama ◽  
Chisaki Ikeda ◽  
Koki Wakabayashi ◽  
Satoru Ato ◽  
Riki Ogasawara
Keyword(s):  
Protein Synthesis ◽  
Resistance Exercise ◽  
Muscle Contraction ◽  
High Intensity ◽  
Gastrocnemius Muscle ◽  
Muscle Protein ◽  
Muscle Protein Synthesis ◽  
Target Of Rapamycin ◽  
Mechanistic Target Of Rapamycin ◽  
Mtorc1 Activation

High-intensity muscle contraction (HiMC) is known to induce muscle protein synthesis, a process in which mechanistic target of rapamycin (mTOR) is reported to play a critical role. However, the mechanistic details have not been completely elucidated. Here, we investigated whether Akt plays a role in regulating HiMC-induced mTORC1 activation and muscle protein synthesis using a rodent model of resistance exercise and MK2206 (an Akt kinase inhibitor). The right gastrocnemius muscle of male C57BL/6J mice aged 10 wk was isometrically contracted via percutaneous electrical stimulation (100 Hz, 5 sets of 10 3-s contractions, 7-s rest between contractions, and 3-min rest between sets), while the left gastrocnemius muscle served as a control. Vehicle or MK2206 was injected intraperitoneally 6 h before contraction. MK2206 inhibited both resting and HiMC-induced phosphorylation of Akt1 Ser-473 and Akt2 Ser-474. MK2206 also inhibited the resting phosphorylation of p70S6K and 4E-BP1, which are downstream targets of mTORC1; however, it did not inhibit the HiMC-induced increase in phosphorylation of these targets. Similarly, MK2206 inhibited the resting muscle protein synthesis, but not the resistance exercise-induced muscle protein synthesis. On the basis of these observations, we conclude that although Akt2 regulates resting mTORC1 activity and muscle protein synthesis, HiMC-induced increases in mTORC1 activity and muscle protein synthesis are Akt-independent processes. NEW & NOTEWORTHY Akt is well known to be an upstream regulator of mechanistic target of rapamycin (mTOR) and has three isoforms in mammals, namely, Akt1, Akt2, and Akt3. We found that high-intensity muscle contraction (HiMC) increases Akt1 and Akt2 phosphorylation; however, HiMC-induced increases in mTORC1 activity and muscle protein synthesis are Akt-independent processes.

scholarly journals Membrane targeting of the small GTPase Rab9 is accompanied by nucleotide exchange

Nature ◽  
1994 ◽  
Vol 369 (6475) ◽  
pp. 76-78 ◽  
Author(s):  
Thierry Soldati ◽  
Allan D. Shapiro ◽  
A. Barbara Dirac Svejstrup ◽  
Suzanne R. Pfefffer
Keyword(s):  
Small Gtpase ◽  
Membrane Targeting ◽  
Nucleotide Exchange

scholarly journals Skeletal Muscle mTORC1 Activation Increases Energy Expenditure and Reduces Longevity in Mice

2019 ◽  
Author(s):  
Erin J. Stephenson ◽  
JeAnna R. Redd ◽  
Detrick Snyder ◽  
Quynh T. Tran ◽  
Binbin Lu ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Energy Expenditure ◽  
High Fat Diet ◽  
High Fat ◽  
Constitutive Activation ◽  
Mechanistic Target Of Rapamycin ◽  
Systemic Insulin Resistance ◽  
Mtorc1 Signaling ◽  
Futile Cycling ◽  
Mtorc1 Activation

AbstractThe mechanistic target of rapamycin (mTORC1) is a nutrient responsive protein kinase complex that helps co-ordinate anabolic processes across all tissues. There is evidence that signaling through mTORC1 in skeletal muscle may be a determinant of energy expenditure and aging and therefore components downstream of mTORC1 signaling may be potential targets for treating obesity and age-associated metabolic disease. Here, we generated mice with Ckmm-Cre driven ablation of Tsc1, which confers constitutive activation of mTORC1 in skeletal muscle and performed unbiased transcriptional analyses to identify pathways and candidate genes that may explain how skeletal muscle mTORC1 activity regulates energy balance and aging. Activation of skeletal muscle mTORC1 produced a striking resistance to diet-and age-induced obesity without inducing systemic insulin resistance. We found that increases in energy expenditure following a high fat diet were mTORC1-dependent and that elevated energy expenditure caused by ablation of Tsc1 coincided with the upregulation of skeletal muscle-specific thermogenic mechanisms that involve sarcolipin-driven futile cycling of Ca2+ through SERCA2. Additionally, we report that constitutive activation of mTORC1 in skeletal muscle reduces lifespan. These findings support the hypothesis that activation of mTORC1 and its downstream targets, specifically in skeletal muscle, may play a role in nutrient-dependent thermogenesis and aging.

scholarly journals mTORC1 in the orbitofrontal cortex promotes habitual alcohol seeking

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Nadege Morisot ◽  
Khanhky Phamluong ◽  
Yann Ehinger ◽  
Anthony L Berger ◽  
Jeffrey J Moffat ◽  
...  
Keyword(s):  
Orbitofrontal Cortex ◽  
Heavy Alcohol ◽  
Mechanistic Target Of Rapamycin ◽  
Heavy Alcohol Use ◽  
Habitual Behavior ◽  
Habitual Responding ◽  
Mtorc1 Activation ◽  
Outcome Devaluation ◽  
Alcohol Seeking ◽  
Alcohol Dependent

The mechanistic target of rapamycin complex 1 (mTORC1) plays an important role in dendritic translation and in learning and memory. We previously showed that heavy alcohol use activates mTORC1 in the orbitofrontal cortex (OFC) of rodents (Laguesse et al., 2017a). Here, we set out to determine the consequences of alcohol-dependent mTORC1 activation in the OFC. We found that inhibition of mTORC1 activity in the OFC attenuates alcohol seeking and restores sensitivity to outcome devaluation in rats that habitually seek alcohol. In contrast, habitual responding for sucrose was unaltered by mTORC1 inhibition, suggesting that mTORC1’s role in habitual behavior is specific to alcohol. We further show that inhibition of GluN2B in the OFC attenuates alcohol-dependent mTORC1 activation, alcohol seeking and habitual responding for alcohol. Together, these data suggest that the GluN2B/mTORC1 axis in the OFC drives alcohol seeking and habit.

scholarly journals Weak membrane interactions allow Rheb to activate mTORC1 signaling without major lysosome enrichment

2019 ◽  
Vol 30 (22) ◽  
pp. 2750-2760 ◽  
Author(s):  
Brittany Angarola ◽  
Shawn M. Ferguson
Keyword(s):  
Endoplasmic Reticulum ◽  
Subcellular Localization ◽  
Membrane Interactions ◽  
Systematic Analysis ◽  
Functional Assays ◽  
Mtorc1 Signaling ◽  
Mtorc1 Activation ◽  
Mtor Complex 1 ◽  
The Relationship ◽  
Caax Motif

Stable localization of the Rheb GTPase to lysosomes is thought to be required for activation of mTOR complex 1 (mTORC1) signaling. However, the lysosome targeting mechanisms for Rheb remain unclear. We therefore investigated the relationship between Rheb subcellular localization and mTORC1 activation. Surprisingly, we found that Rheb was undetectable at lysosomes. Nonetheless, functional assays in knockout human cells revealed that farnesylation of the C-terminal CaaX motif on Rheb was essential for Rheb-dependent mTORC1 activation. Although farnesylated Rheb exhibited partial endoplasmic reticulum (ER) localization, constitutively targeting Rheb to ER membranes did not support mTORC1 activation. Further systematic analysis of Rheb lipidation revealed that weak, nonselective, membrane interactions support Rheb-dependent mTORC1 activation without the need for a specific lysosome targeting motif. Collectively, these results argue against stable interactions of Rheb with lysosomes and instead that transient membrane interactions optimally allow Rheb to activate mTORC1 signaling.

The GATOR–Rag GTPase pathway inhibits mTORC1 activation by lysosome-derived amino acids

Science ◽  
2020 ◽  
Vol 370 (6514) ◽  
pp. 351-356
Author(s):  
Geoffrey G. Hesketh ◽  
Fotini Papazotos ◽  
Judy Pawling ◽  
Dushyandi Rajendran ◽  
James D. R. Knight ◽  
...  
Keyword(s):  
Amino Acids ◽  
Cell Growth ◽  
Target Of Rapamycin ◽  
Lysosomal Degradation ◽  
Oncogenic Ras ◽  
Mechanistic Target Of Rapamycin ◽  
Independent Mechanism ◽  
Guanosine Triphosphatase ◽  
Rag Gtpase ◽  
Mtorc1 Activation

The mechanistic target of rapamycin complex 1 (mTORC1) couples nutrient sufficiency to cell growth. mTORC1 is activated by exogenously acquired amino acids sensed through the GATOR–Rag guanosine triphosphatase (GTPase) pathway, or by amino acids derived through lysosomal degradation of protein by a poorly defined mechanism. Here, we revealed that amino acids derived from the degradation of protein (acquired through oncogenic Ras-driven macropinocytosis) activate mTORC1 by a Rag GTPase–independent mechanism. mTORC1 stimulation through this pathway required the HOPS complex and was negatively regulated by activation of the GATOR-Rag GTPase pathway. Therefore, distinct but functionally coordinated pathways control mTORC1 activity on late endocytic organelles in response to distinct sources of amino acids.

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